1. Field of the invention:
This invention relates to a conductive fabric with a large spreading ratio made with crimped conductive fibers, a method for the manufacture of this conductive fabric, and a conductive sheet and film made with the use of the said conductive fabric.
2. Description of the prior art:
The trays, containers, packaging, etc., used for the packing or transportation of electronic devices such as semiconductor devices, etc., that are in danger of being damaged in their functioning by the invasion of static electricity or noise, and the filing cases, etc., that are used to store recording materials such as magnetic disks, magnetic cards, etc., which are sensitive in the same way to static electricity and noise, must be prevented from being charged with electricity, and moreover need conductivity to shield their contents from electromagnetic waves. As the containers mentioned above, molded plastics containing carbon black and conductive fillers such as short metal fibers, etc., have been put into practical use. However, to lend the desired conductivity to such plastic, it is necessary to use a large quantity of conductive filler, which causes the molded parts to be molded in an unsatisfactory way and causes a decrease in the mechanical strength.
To eliminate these problems, an inexpensive method for manufacturing conductive sheets for wrapping of parts such as IC, etc., has been proposed by, for example, Japanese Laid Open Patent Publications Nos. 58-155917 and 58-166035, in which a non-woven fabric, a knit, or a textile, made from a fiber mixture of conductive fiber and thermoplastic fibers is disposed on a base and heated to a temperature above the temperature at which the thermoplastic fibers melt, to adhere itself thereby to the base, resulting in a conductive sheet for wrapping of parts such as IC, etc.
However, the conductive textile of the sheets made in the way described above cannot stretch, and when the said sheet is treated by deep drawing processing by vacuum forming or pressure forming, the sheet is stretched and the conductive textile is ripped, which causes lowering of the conductivity of the resulting molded article. Moreover, in sheets made from a non-woven fabric or a knit manufactured by the method described above, a certain amount of stretching is made possible by the structure of the non-woven fabric and the knit, but when the sheet is treated by deep drawing processing by which the surface area before and after the non-woven fabric and the knit is stretched (that is, the spreading ratio) becomes 2 times or more, the conductive non-woven fabric or knit is ripped in the same way as with the textile, which causes the lowering of the conductivity of the resulting molded article. For this reason, there is the problem that it is not possible to make a container, etc., with a deep bottom that has superior conductivity from a flat sheet with a conductive fabric therein.